Optical particle counters are currently the primary detection tool for most industrially controlled particle contamination. Classifying by particle sizes, particles includes 5 μm particles, 2 μm particles, 1 μm particles, 0.5 μm particles, 0.2 μm particles, 0.1 μm particles, 0.05 μm particles, and even smaller, nano-sized particles.
Optical particle counters currently used to detect micron-sized particles (above 2 μm) are based on the principle of the light blockage method. As shown in FIGS. 1 and 2, the existing light-blockage particle counter comprises a light source 201, an optical component 202, a flow cell 203, a photoelectric detector 204, a preamplifier 205, a comparator 206, and a counter 207. By means of the optical component 202 (including a convex lens, a cylindrical mirror, etc.), the circular spot generated by the light source 201 is converted into a line spot to be irradiated on the flow channel 208 within the flow cell 203, thereby forming a linear detection area 210, and then when the particles 200 pass through the detection area, scattered light is generated to be irradiated on the photoelectric detector 204 to generate current pulse signals 211 and 212 having different amplitudes and pulse widths, and then the current pulse signals are converted into voltage pulse signals via the preamplifier 205, and then into digital signals 213 and 214 via the comparator 206, which are input into the counter 207, and the counter 207 screens and counts the pulse signals according to the amplitudes of the pulse signals. FIG. 3 is a view showing a pulse signal scattered by particles passing through the detection area 210 in the flow cell 203 obtained by the existing particle counting system based on the light blockage method, which visually shows the conversion process of optical signals to electrical signals during the particle detection process in the light-blockage particle counter system.
The existing light-blockage particle counter converts the light emitted by the light source into a line light source through the optical component, and the main purpose thereof is to make the light source distribute uniformly in the detection area, thereby ensuring the sensitivity and resolution of the detection. However, the optical structures of the existing optical particle counter and system are relatively complicated, have a low light source utilization rate, and only can utilize a part of the light beam converted by the optical module in the light source.
The optical particle counter for detecting sub-micron-sized and nano-sized particles (below 1 μm) is based on the principle of light scattering, and generally adopts a circular spot, which can improve the utilization rate of the light source, increase the scattered light intensity of the particles, and improve the sensitivity of the system. However, due to the uneven distribution of the optical density of the light source spot, the resolution and sensitivity of the system on particles are greatly reduced, which seriously affects the test accuracy of the system.